cryptanalysis, vigenere cipher

The vigenere cipher shifts the letters of the plaintext, according to the
corresponding letter of a key phrase.
The key phrase is typically short (it must be easily memorized
by the sender and the receiver).
If the key phrase is exhausted, it is repeated again and again.
Addition of letters is done mod 26, i.e. 'z' + 'b' = 'b'.

Example:

ilovecryptography

with key phrase

secret

becomes

apqmivjcrkszjeryc

(since 'i'+'s'='a', 'l'+'e'='p', ... , 'c'+'t'='v', and then 'r'+'s'='j' and so forth)

remark: note that the shift cypher is a special case of the vigenere
cipher, namely with a key phrase of just one letter.

You may try cryptanalyzing the following texts,
which were obtained from an english text by a substitution cipher: